1. Field of the Invention
The present invention relates to a dielectric ceramic and a laminated ceramic capacitor, and particularly relates to a dielectric ceramic suitable for use in a thin layer, large capacity, laminated ceramic capacitor and a laminated ceramic capacitor constituted using the dielectric ceramic.
2. Description of the Related Art
Mentioned as one of effective measures for satisfying demands for a reduction in the size and an increase in the capacity of a laminated ceramic capacitor is to reduce the thickness of the dielectric ceramic layers provided in the laminated ceramic capacitor. However, the electric field strength per layer of the dielectric ceramic layer becomes higher with the reduction in the thickness of the dielectric ceramic layer. Therefore, the dielectric ceramic used has been required to have more reliability, and particularly higher life characteristics in a load test.
As the dielectric ceramic constituting the dielectric ceramic layer of the laminated ceramic capacitor, a BaTiO3 dielectric ceramic has been used in many cases. In the BaTiO3 dielectric ceramic, elements, such as rare earth elements or Mn, are added as accessory components in order to achieve favorable reliability and various electrical characteristics.
For example, Japanese Unexamined Patent Application Publication No. 10-330160 (Patent Document 1) discloses a dielectric ceramic having a core shell structure containing, as the main component, ABO3 (A always contains Ba and sometimes contains at least one of Ca and Sr. B always contains Ti and sometimes contains at least one of Zr, Sc, Y, Gd, Dy, Ho, Er, Yb, Tb, Tm, and Lu.), in which at least one of Mn, V, Cr, Co, Ni, Fr, Nb, Mo, Ta, and W is almost uniformly dispersed throughout the particles. Patent Document 1 also discloses an Example in which Mg is a shell component and the Mg is not dispersed in the core and is dispersed only in the shell portion.
However, even when the dielectric ceramic described in Patent Document 1 is used, the reliability and particularly the life characteristics in a load test are insufficient when there is a further reduction in the thickness of the dielectric ceramic layer, and thus a further improvement has been demanded.